Guidewires are used in numerous catheterization procedures as an aid to placement of a catheter in a selected site within the human body. The catheter is constructed to perform a particular procedure at that internal site. For example, among the more common uses of guidewires is in the catheterization of blood vessels for purposes of diagnosis or treatment. In a common type of vascular catheterization procedure, the guidewire first is inserted, usually percutaneously, into the patient's vascular system and is manipulated and advanced to the target site. The catheter then is threaded over and advanced along the guidewire, with the guidewire serving to guide the catheter directly to the target site. By way of further example, a number of catheterization procedures are performed with respect to the coronary arteries, including diagnostic catheterization procedures in which an angiographic catheter is advanced through the patient's arteries to the entrance to the coronary arteries. A radiopaque contrast liquid then is injected through the angiographic catheter into the coronary arteries under X ray fluoroscopy, so that the anatomy of the patient s coronary arteries may be observed visually. Once the coronary anatomy has been determined, the physician may perform additional catheterization procedures, including percutaneous transluminal coronary angioplasty (PTCA), in which a balloon catheter or other angioplasty catheter is advanced into the coronary arteries to widen an obstructed portion of the artery.
In a typical PTCA procedure, an angioplasty catheter, which may be in the form of an elongate flexible shaft with an inflatable balloon at its distal end, is advanced from a percutaneous puncture site in the patient s femoral artery through the patient's arteries to and into the coronary arteries. The catheter is guided to the target site of the obstruction by use of a slender guidewire which initially is advanced into and manipulated through the coronary arteries, in advance of the dilatation catheter. Once the distal end of the guidewire is in place within the obstruction, the catheter then is advanced over the guidewire which guides the catheter directly to the obstruction to place its balloon within the obstruction. The balloon then is inflated to dilate the obstructed portion of the artery, thereby enlarging the flow area through the artery.
Guidewires used with PTCA catheters are of special design. Although they are extremely slender, of the order of 0.010"-0.018" diameter, they nevertheless must be capable of transmitting rotation from the proximal end of the guidewire to the distal end in order that the physician may steer the guidewire and manipulate it to the target site in the intended coronary artery. Additionally, the distal end of the guidewire must be very flexible in order that the distal portion of the guidewire can pass through sharply curved, highly tortuous coronary anatomy as well as to provide a soft, floppy distal tip that will not injure the artery or its delicate inner surface.
It is desirable that the physician be able to feel the response of the guidewire as it is manipulated and advanced through the patient's arteries. By having increased sensitivity to its movement, the physician may better control the guidewire. In order to enhance that sensitivity, it is desirable that the guidewire and dilatation catheter through which the guidewire passes, have low frictional resistance without sacrificing the degree to which the guidewire displays other desirable characteristics. It also is among the desirable features of a guidewire that it have sufficient column strength so that it can be pushed without buckling. The guidewire should have sufficient torsional rigidity to transmit torque sufficiently to enable the rotated position of the distal end of the guidewire to be controlled from its proximal end, where the physician grasps the guidewire. These features must be incorporated into a guidewire which also displays a sufficiently high degree of flexibility at its distal end in order to conform safely to sharp bends and tortuous coronary anatomy.
In addition to the foregoing, it also is important that a distal segment of the guidewire is highly radiopaque so that its position can be observed under X-ray fluoroscopy. That enables the physician to observe the location and configuration of the distal end of the guidewire as the guidewire is manipulated and advanced through the patient's arteries. In procedures, such as coronary angioplasty, in which a catheter is advanced through the patient's arteries, it often is the practice to inject radiopaque contrast liquid periodically into the artery so that the shape and path of the artery may be visualized fluoroscopically. With conventional guidewires used in PTCA, the radiopacity of the guidewire coil may be so dense as to visually obstruct part of the artery which the physician may desire to view when the contrast liquid is injected. For use in such instances, it would be desirable for the guidewire to be only partially highly radiopaque, that is, to form a light but visible gray shadow in some portions and a heavy, dark fluoroscopic image on another.
It is among the general objects of the invention to provide a guidewire that satisfies all of the above objectives.